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Cerebral blood volume (CBV): the volume of blood per unit of brain tissue Cerebral blood flow (CBF): the volume of blood flow per unit of brain tissue per minute Mean transit time (MTT): defined as the time difference between the arterial inflow and venous outflow Time to peak (TTP): The time from the beginning of contrast material injection to the maximum concentration of contrast material within a region of interest

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Steps in CT Perfusion Data Postprocessing Freehand or automated placement of an ROI over an input artery to obtain the arterial time-attenuation curve or arterial input function Freehand or automated placement of an ROI over an input vein to obtain the venous time-attenuation curve Generation of the arterial and venous time-attenuation curves

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Perfusion Parameters MTT- Deconvolution of arterial and tissue enhancement curve CBV- calculated as the area under the curve in a parenchymal pixel divided by the area under the curve in an arterial pixel. CBF- using the central volume equation: CBF= CBV/MTT Since the input artery is usually smaller than the input vein, the venous ROI serves to correct for volume averaging in the arterial ROI.